Restarted hemodialysis. Taking aspirin. Still at the risk of stroke. What blood thinner work best? Side effects

My uncle had a stroke in Nov. He also restarted hemodialysis post failed transplant. After his stroke he was started on aspirin. He was admitted for GI bleed and a RBC count of 5.0. After a transfusion it is now 7.0mg. Is he still at risk for a stroke with this low RBC count? If so what type of blood thinner would work best for his condition? Just really need to know what blood thinners have the less side effects/